This paper presents an original sensor that can measure the relative dielectric constant of gases, or, if the permittivity of the gas is known, the sensor can measure the pressure of a chamber filled with the gas. The sensor is demonstrated to operate through 460 °C and 90 atm (1322 psi) to allow gas property measurements throughout a range of harsh environments. The sensor is demonstrated with permittivity measurements of N2 across the X-Band as a function of gas density at 25 °C and of Venus atmosphere gases at 460 °C.